1. Field of the Invention
The present invention relates to nuclear magnetic resonance devices for examining a subject by inducing and measuring magnetic resonance signals in the patient, and in particular to a means for homogenizing the fundamental magnetic field in such an apparatus.
2. Description of the Prior Art
A basic nuclear magnetic resonance tomograph apparatus is described in U.S. Pat. No. 3,564,398 which includes respective sets of coils for generating fundamental and gradient magnetic fields in which an examination subject is disposed, a radio-frequency means for applying RF pulses to the subject and for acquiring the nuclear magnetic resonance signals resulting from the pulses from the subject. This apparatus is suitable for exciting hydrogen atom nuclei of the examination subject and for displaying the proton distribution of a selected slice of the subject. It is necessary that disturbances which occur in the fundamental field be corrected in order to obtain good image quality. A number of current-permeated correction coils, referred to as shim coils, are provided for the purpose of homogenizing the fundamental field.